Process of making rustless iron and similar alloys



Patented Sept. 9, 1924.

barren stares FREDERICK M. BECKET, OF NEW YORK, N. Y., ASSIGNOR TO ELECTRO' METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA.

PROCESS OF MAKING RUSTLESS IRON AND SIMILAR ALLOYS.

No Drawing.

To all whom it may concern:

Be it known that I, FREDERICK M. BECKET, a citizen of United States of America, residing at New York, N. Y., in the county of New York and State of New York, have invented certain new and useful Improvements in Processes of Making Rustless Iron and Similar Alloys, of which the following is a specification.

.This invention relates primarily to the manufacture of iron-chromium alloys of the general type known to the trade as rustless iron, and comprises a process whereby these and similar alloys, hereinafter referred to as rust-resisting chromium alloys, may be prepared directly from the ore in an electric furnace employing carbon electrodes.

As is now well understood in this art, rust-less iron isa readily workable alloy usually containing about 815 per cent of chromium, although either higher or lower percentages may be used. It is necessarily a low-carbon product, the carbon content preferably not exceeding 0.1 per cent: The balance is principally iron, usually with small percentages of silicon and manganese and at times of other metals. Such alloys have been usually prepared in' the past by the direct addition of low-carbon chromium metal or low-carbon ferro-chromium to an iron bath; but various efforts have heretofore been made to prepare this and similar alloys by direct reduction of chrome ores into an iron bath, employing a metallic reducing agent such as aluminum, Silicon or ferrosilicon. In such cases the heat neces sary to initiate and maintain the reaction is usually derived from the metalbath in an open-hearth furnace, crucible or the like, or from a slag overlying such bath; and difliculty is encountered in maintaining a suflicient temperature to permit a high reaction efliciency to be obtained. It is quite possible however to maintain a sufiicient temperature for this purpose in electric furnaces of various types but even in such case it has been found that ingots poured from metal baths which have been maintained for considerable periods of time at the high temperatures which are essential for a satisfactory and uniform recovery of chromium often exhibit a strong tendency to rise or pufi' in the molds. The causes underlying this tendency are not certainly known, but it is known that they are associated with the subjection of the- Serial No. 600,684.

metal baths to very high temperatures for considerable perlods of time, and that the tendency of the poured metal to rise is not overcome by the use of the usual deoxidizers,"

othcr source of low carbon iron or steel. I am able in accordance with my novel proc css, to use carbon or graphite electrodes, while nevertheless keeping the carbon content of the product within the necessary limits, and if desired well below 0.1 per cent.

' The product is moveovcr of excellent grade,

and in particular may be so prepared as to be practically free from the troublesome tendency to rise in the molds.'

In all prior processes of making rustless iron direct from the ore, so far as I am aware, the chrome ore has been reduced into a preformed metal bath, which contained the great bulk of the iron component of the product, the chrome ore being reduced either directly within the bath, or in a slag overlying the bath. In either case the bath was necessarily maintained at the high temperature requisite for the chromium reduction throughout the entire period of the reducing reaction; and as already stated, this is the condition which has led in the past to rising ingots, if the temperature has been sufficiently high to insure good recovery of chromium; or at lower temperatures, to low and irregular chromium recoveries.

According to my novel process in its preferred embodiment I carry out the operation in two stages, which merge into a continuous procedure. In the first stage the chrome ore is reduced by means of a non-carbonaceous reducing agent which may be aluminum, or silicon, or ferrosilicon, or, and preferably, a chromium-silicon alloy such as chrome-silicon or ferro-chrome-silicon. The advantage of using these last mentioned reducing agents will appear hereinafter. This reducing operation is carried out rapidly and with a lowed in the same or other furnace by a sec- 0nd and lower temperature operation whereby the high-chromium low-carbon alloy resulting from the first operating stage is diluted by means of low-carbon iron, derived high energy input and is immediately fol- 106 usually from soft iron or low-carbon steel scrap. By proceeding in this way the bulk of the alloy bath is at no time subjected to the very high temperatures necessary for eflicient chrome reduction, and the tendency of the ingots to rise is obviated.

Following is a. specific example in accordance with my invention, it being understood however that the invention is not limited to the particular manipulations or to the special type of furnace referred to herein:

The furnace may be of the tilting type provided with a magnesite or other basic 'fluorspar additions.

lining and two depending, adjustable graphite or carbon electrodes of relatively small cross sectional area. I first melt down in this furnace a small quantity of charge comprising for example chromite, a metallic reducing agent (aluminum, silicon, ferrosilicon, chrome-silicon or ferro-chrome silicon) and a flux, usually lime, with or without Thereby I establish a shallow slag bath, underlaid by such small quantity of metal as may have been reduced in course of its formation. This operation may be initiated in any desired manner, such for example as by laying a train of metal fragments between the electrodes and areing to this train; or by arcing to a graphite pencil or starting-rod lying between the elec- L trodes, and removing this rod by means of tongs as soon as a conductive bath has been established. This starting operation is preferably carried out with a reactance in the electric circuit, using only sufficient energy to form the fluid conductive starting bath. When this latter condition is secured the electrodes are adjusted above and out of physical contact with the slag, and by the use of a sufliciently high impressed voltage, usually 15025O volts according to the fusibility and electrical conductivity of the slag,

unsubmerged arcs representing a high energy input are maintained between the electrodes and the slag. Further quantities of charge of like composition are now fed to the furnace until the entire quantity of chromium for the melt has been reduced in the form of a high-chromium low-carbon alloy. llf de sired, pure chrome oxid might of course be used at this stage with fluxes; adapted to yield a basic slag bath, but the use of chrome ore as described isas a rule equally satisfac-' tory and of course more economical.

'ljhe bath should preferably be maintained basic throughout the operation. Since the s1l1con component of the reducing agent undergoes oxidation to the acid oxid, silica, it is of course necessary to provide in the charge suficient basic oxids, as lime, magnesla or alumina, to neutralize the silica and establish the desired basicity. Accordingly basic fluxes are used whenever the basic oxid content of the ore is insuflicient. These basic slags are relatively highly conductive and the slag at the lower temperature.

render possible the maintenance at practical Voltages of long unsubmerged arcs as above described.

It is important to minimize so far as practicable the time required for the chromium reduction, because of the tendency of the carbon content of the product to increase when the smelting is unduly prolonged. As already explained this may be accomplished under otherwise suitable operating conditions by the use of high temperature and a high rate of energy input. A further shortening of the time is brought about by the use, as the reducing agent, of chromium-- silicon compounds, as chrome-silicon or ferro-chr ome-silicon. Both of these alloys, when their silicon content is sufficiently high. are characteristically low in carbon; and

their chromium content is of course directly available for the enrichment of the bath.

Accordingly I prefer to use such chromesilicon alloys as the reducing agent for chrome ore in the preparation of rustless iron, and my invention contemplates such use broadly in this art, irrespective of the type of furnace employed 0120f the conditions under which the reduction is accomplished.

Following the chomium-reducing operation the low-carbon iron necessary to dilute the melt to the desired chromium content is are not required, and the furnace tempera ture is lowered correspondingly. It is not practicable to state the operating temperatures during either operating .stage in terms of precise thermometric degrees, as exact measurement is difficult or impracticable; but it will be a suliicient guide for the experienced metallurgist to state that the temperature during the chromium-reducing stage is preferably as high as can be practically maintained, employing for example upward of 150 volts for two arcs inseries; while during the second, or diluting stage, the temperature is merely, suflicient for the melting down of the soft iron and the maintenance of a fluid bath and slag. If desired fluorspar or other suitable flux may be added at this point to insure suflicient fluidity of These temperatures probably approximate 1800 1900 C. during the reducing stage, and 1600 C. during the diluting stage. Stron ly reducing conditions are maintained throughout, more especially during the first ins stage, and any marked tendency of the metal to rise in the molds may be regarded as usually indicative ,of excessive temperatures during the dilution. I have found it desirable to use sufiicient of the reducing agent, as silicon, so that some excess will remain in the product at the close of the first stage,

thereby insuring reducing conditions during the second stage, and a proper slicon contentin the finished (diluted) product. It is one of the advantages of my dilution method that it lends itself to this procedure. Excessive local temperatures duet-o the arcs may be avoided by the use of slag baths of suificient depth. At intervals the alloy is tapped off, leaving in the furnace a small quantity of metal'and slag to initiate the next operation.

The process as described above is also applicable in case it is desired to dilute the low-carbon chromium or ferrochromium initially perpared with a metal other than iron, as for example nickel or cobalt, or mixtures of iron with nickel or cobalt, or with nickel and cobalt. Such diluting metals are collectively referred to as metals of the iron-group.

Also, the process may be readily adapted to the preparation of so-called stainless steels which are of similar composition as respects iron and chromium, but of decidedly higher carbon content. For'this purpose it is merely necessary properly to carburize the bath, for example by the addition of high carbon ferrochromeat or near the end of the heat or even in the ladle, or to employ steel scrap of the proper carbon content as the. diluting material.

It will of course be understood that the usual steel practice may be employed with respect to the use of manganese or other deoxidizing, scavenging or alloying additions,the' employment of finishing slags, etc.

Typical analyses of rustless iron perpared according to this invention are:-

Chromium. Silicon. Carbon.

the balance substantially all iron. But as already explained my process lends itself to the preparation of widely varying compositions of low-carbon alloys of the general type comprising chromium and a metal or metals of the iron group.

I claim:

1. The hereindescribed continuous process of preparing rust-resisting chromium alloys comprising reducing an ore of chromium at a high temperature by means of a metallic reducing agent, out of contact with the bulk of the ferrous component of the alloy,

thereby producing a metallic product high in chromium and low in carbon; and then diluting the resulting melt by means of air iron-group metal at a substantially lower temperature. I

of preparing rust-resisting chromium alloys, comprising reducing an ore of chromium at a high temperature by means of. a silicon-containing reducing agent,out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resultingmelt by means of an iron-group .metal at a substantially lower temperature.

2. The hereindescribed, continuous process 3. The hereindescribed continuous process of preparing rust-resisting chromium alloys. comprising reducing an ore of chromium at a high temperature by means of a reducing agent comprising silicon and chromium, out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high inchromium and lowin carbon; and diluting the resulting melt by means of an iron-group metal at a sub stantially lower temperature.

4. The hereindescribed continuous process of preparing rust-resisting chromium alloys, comprising reducing a chromium ore in a basic slag bath by means of a metallic reducing agent and electrical energy supplied.

through an unsubmerged arc. said reduction being efi'ected out of contact with the bulk of the ferrous 'componentof the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting melt by means of an irongroup metal.

5. The hereindescribed continuous proces:=

of preparing rust-resisting chromium alloys. comprising reducing a chromium ore in a basic slag bath by means of a. silicon-containing reducing agent and electrical energv supplied through an unsubmerged are, said reduction being eifected out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium andlow in carbon; and diluting the resulting melt by means of an iron-group metal.

6. The hereindescribed continuous process of preparing rust-resisting chromium alloys, comprising reducing a chromium ore in a basic slag bath by means of a reducing agent comprising silicon and chromium and electrical energy supplied through an unsubmerged are, said reduction being eifected out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting of preparing low-carbon alloys containing chromium and a metal of the iron-group,

.comprising reducing an ore of chromium at a high temperature by means of a metallic reducing agent, but of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting melt by means of an iron-group metal at a substantially lower temperature.

8. The hereindescribed continuous process of preparing low-carbon alloys containing chromium and a metal of the iron-group, comprising reducing an ore of chromium at a high temperature by means of a siliconcontaining reducing agent, out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting melt by means of an iron-group metal at a substantially lower I ess of preparing low-carbon alloys containing chromium and a metal of the iron-group,

comprising reducing a chromium ore in a basic slag bath by means of a metallic reducing agent and electrical energy supp-lied through an unsubmerged are, said reduction being efl'ected out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting melt by means of an iron-group metal.

11. The hereindescribed continuous process of preparing low-carbon alloys containing chromium and a metal of the iron-group, comprising reducing a chromium ore in a basic slag bath by means of a silicon-containing reducing agent and electrical energy supplied through an unsubmerged arc, said reduction being effected out of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic product high in chromium and low in carbon; and diluting the resulting melt to the desired degree by means of an iron-group metal.

12. The hereindescribed continuous proc ess of preparing low-carbon alloys containing chromium and a metal of the iron-group comprising reducing a chromium ore in a basic slag bath by means of a reducing agent comprising silicon and chromium and eleo trical energy supplied through an unsub merged arc, said reduction being efl'ected out. of contact with the bulk of the ferrous component of the alloy, thereby producing a metallic, product high in chromium and low in carbon; and diluting the resulting melt by means of an iron-group metal.

13. In a process of making rust-resisting chromium alloys the step comprising reacting upon an ore of chromium with a reducing agent comprising chromium and silicon.

14. In a process of making rust-resisting chromium alloys the steps comprising establishing an unsubmerged carbon arc to the surface of a basic slag bath, and reducing an ore of chromium therein by means of a metallic reducing agent.

15. In a process of making rust-resisting chromium alloys the steps comprising establishing an unsubmerged carbon arc to the surface of a basic slagbath, and reducing an ore of chromium therein by means of a. silicon-containing reducin agent.

16. In a process of ma ing rust-resisting chromium alloys the steps comprising estab lishing an unsubmerged carbon are to the surface of a basic slag bath, and reducing an ore of chromium therein by means of a reducing agent comprising chromium and silicon.

In testimony whereof, I a my signature.

FREDERICK M. BECKET. 

